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/*
* Copyright 2014-2022 Rudy De Busscher (https://www.atbash.be)
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package be.atbash.util.reflection;
import be.atbash.util.PublicAPI;
import be.atbash.util.SecurityReview;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.io.IOException;
import java.io.InputStream;
import java.lang.reflect.Constructor;
import java.net.URL;
import java.util.*;
/**
* Utility class used to conveniently interact with Classes, such as acquiring them from the
* application ClassLoaders and instantiating Objects from them.
* Class original found in Apache Shiro but modified for enhanced functionality.
*/
@PublicAPI
public final class ClassUtils {
/**
* Private internal log instance.
*/
private static final Logger log = LoggerFactory.getLogger(ClassUtils.class);
/**
* The Thread context class loader.
*/
private static final ClassLoaderAccessor THREAD_CL_ACCESSOR = new ExceptionIgnoringAccessor() {
@Override
protected ClassLoader doGetClassLoader() {
return Thread.currentThread().getContextClassLoader();
}
};
/**
* The classloader which has loaded the ClassUtils itself.
*/
private static final ClassLoaderAccessor CLASS_CL_ACCESSOR = new ExceptionIgnoringAccessor() {
@Override
protected ClassLoader doGetClassLoader() {
return ClassUtils.class.getClassLoader();
}
};
/**
* The System class loader.
*/
private static final ClassLoaderAccessor SYSTEM_CL_ACCESSOR = new ExceptionIgnoringAccessor() {
@Override
protected ClassLoader doGetClassLoader() {
return ClassLoader.getSystemClassLoader();
}
};
/**
* Singleton type class.
*/
private ClassUtils() {
}
/**
* Returns the specified resource by checking the current thread's
* {@link Thread#getContextClassLoader() context class loader}, then the
* current ClassLoader (ClassUtils.class.getClassLoader()), then the system/application
* ClassLoader (ClassLoader.getSystemClassLoader(), in that order, using
* {@link ClassLoader#getResourceAsStream(String) getResourceAsStream(name)}.
*
* @param name the name of the resource to acquire from the classloader(s).
* @return the InputStream of the resource found, or null if the resource cannot be found from any
* of the three mentioned ClassLoaders.
*/
public static InputStream getResourceAsStream(String name) {
InputStream is = THREAD_CL_ACCESSOR.getResourceStream(name);
if (is == null) {
if (log.isTraceEnabled()) {
log.trace("Resource [" + name + "] was not found via the thread context ClassLoader. Trying the " +
"current ClassLoader...");
}
is = CLASS_CL_ACCESSOR.getResourceStream(name);
}
if (is == null) {
if (log.isTraceEnabled()) {
log.trace("Resource [" + name + "] was not found via the current class loader. Trying the " +
"system/application ClassLoader...");
}
is = SYSTEM_CL_ACCESSOR.getResourceStream(name);
}
if (is == null && log.isTraceEnabled()) {
log.trace("Resource [" + name + "] was not found via the thread context, current, or " +
"system/application ClassLoaders. All heuristics have been exhausted. Returning null.");
}
return is;
}
/**
* Return the list of URLs for the resource. It tries to determine is the resource is available on the Thread Context
* Classloader, the Classloader of the {@link ClassUtils} class or the System Classloader.
* @param name the name of the resource to acquire from the classloader(s).
* @return List of URLs pointing to the resource or empty list when resource is not present.
*/
public static List getAllResources(String name) {
Set result = new HashSet<>(THREAD_CL_ACCESSOR.getResources(name));
result.addAll(CLASS_CL_ACCESSOR.getResources(name));
result.addAll(SYSTEM_CL_ACCESSOR.getResources(name));
return new ArrayList<>(result);
}
/**
* Attempts to load the specified class name from the current thread's
* {@link Thread#getContextClassLoader() context class loader}, then the
* current ClassLoader (ClassUtils.class.getClassLoader()), then the system/application
* ClassLoader (ClassLoader.getSystemClassLoader(), in that order. If any of them cannot locate
* the specified class, an UnknownClassException is thrown (our RuntimeException equivalent of
* the JRE's ClassNotFoundException.
*
* @param fqcn the fully qualified class name to load
* @return the located class
* @throws UnknownClassException if the class cannot be found.
*/
public static Class forName(String fqcn) {
Class clazz = THREAD_CL_ACCESSOR.loadClass(fqcn);
if (clazz == null) {
if (log.isTraceEnabled()) {
log.trace("Unable to load class named [" + fqcn +
"] from the thread context ClassLoader. Trying the current ClassLoader...");
}
clazz = CLASS_CL_ACCESSOR.loadClass(fqcn);
}
if (clazz == null) {
if (log.isTraceEnabled()) {
log.trace("Unable to load class named [" + fqcn + "] from the current ClassLoader. " +
"Trying the system/application ClassLoader...");
}
clazz = SYSTEM_CL_ACCESSOR.loadClass(fqcn);
}
if (clazz == null) {
String msg = "Unable to load class named [" + fqcn + "] from the thread context, current, or " +
"system/application ClassLoaders. All heuristics have been exhausted. Class could not be found.";
throw new UnknownClassException(msg);
}
return clazz;
}
/**
* Checks if the fullyQualifiedClassName is available on any classloader.
*
* @param fullyQualifiedClassName The FQCN to check
* @return Is class available or not.
*/
public static boolean isAvailable(String fullyQualifiedClassName) {
try {
forName(fullyQualifiedClassName);
return true;
} catch (UnknownClassException e) {
return false;
}
}
/**
* Creates an instance of the class where it is searched by the algorithm described at the
* {@link ClassUtils#forName(String)} method using the no-arg constructor.
*
* @param fqcn The FQCN to instantiate.
* @param Convenient generic so cast is not needed.
* @return The instantiated class.
* @throws UnknownClassException if the class cannot be found.
* @throws InstantiationException if the class instantiation went wrong.
*/
public static T newInstance(String fqcn) {
return newInstance(forName(fqcn));
}
/**
* Creates an instance of the class where it is searched by the algorithm described at the
* {@link ClassUtils#forName(String)} method with a constructor matching the arguments.
*
* @param fqcn The FQCN to instantiate.
* @param Convenient generic so cast is not needed.
* @param args The arguments for the constructor
* @return The instantiated class.
* @throws UnknownClassException if the class cannot be found.
* @throws InstantiationException if the class instantiation went wrong.
*/
public static T newInstance(String fqcn, Object... args) {
return newInstance(forName(fqcn), args);
}
/**
* Creates an instance of the class using the no-arg constructor.
*
* @param clazz Class which needs to instantiated.
* @param Convenient generic so cast is not needed.
* @return The instantiated class.
* @throws InstantiationException if the class instantiation went wrong.
*/
public static T newInstance(Class clazz) {
if (clazz == null) {
String msg = "Class method parameter cannot be null.";
throw new IllegalArgumentException(msg);
}
try {
return (T) clazz.getDeclaredConstructor().newInstance();
} catch (Exception e) {
throw new InstantiationException("Unable to instantiate class [" + clazz.getName() + "]", e);
}
}
/**
* Creates an instance of the class with a constructor matching the arguments.
*
* @param clazz Class which needs to instantiated.
* @param args The arguments for the constructor
* @param Convenient generic so cast is not needed.
* @return The instantiated class.
* @throws InstantiationException if the class instantiation went wrong.
*/
public static T newInstance(Class clazz, Object... args) {
Class[] argTypes = new Class[args.length];
for (int i = 0; i < args.length; i++) {
// Support for null argument
if (args[i] != null) {
argTypes[i] = args[i].getClass();
}
}
Constructor ctor = getConstructor(clazz, argTypes);
return instantiate(ctor, args);
}
/**
* Match the constructor based on the argument types. But argType items can be null!
* 1. First only exact matches are considered.
*
2. If the first step returns no {@link Constructor}, subtypes are considered.
*
3. When not exactly one {@link Constructor} is found, an {@link NoConstructorFoundException} is thrown.
*
* @param clazz Class for which Constructors must be searched
* @param argTypes List of ClassType of arguments, null values allowed.
* @return Constructor that match the argumentTypes.
* @throws NoConstructorFoundException When no constructor (or multiple) is found which matches the argumentTypes.
*/
static Constructor getConstructor(Class clazz, Class... argTypes) {
return matchConstructor(clazz, argTypes);
}
/**
* Match the constructor based on the argument types. But argType items can be null!
*
1. First only exact matches are considered.
*
2. If the first step returns no {@link Constructor}, subtypes are considered.
*
3. When not exactly one {@link Constructor} is found, an {@link NoConstructorFoundException} is thrown.
*
* @param clazz Class for which Constructors must be searched
* @param argTypes List of ClassType of arguments, null values allowed.
* @return Constructor that match the argumentTypes.
* @throws NoConstructorFoundException When no constructor (or multiple) is found which matches the argumentTypes.
*/
private static Constructor matchConstructor(Class clazz, Class[] argTypes) {
List> constructors = matchAllConstructors(clazz, argTypes, true);
if (constructors.isEmpty()) {
constructors = matchAllConstructors(clazz, argTypes, false);
}
if (constructors.size() != 1) {
throw new NoConstructorFoundException(clazz, argTypes);
}
return constructors.get(0);
}
/**
* Matches all constructors having the argument types. Due to support for null values, multiple constructors can be
* matched.
*
* @param clazz Class for which Constructors must be searched
* @param argTypes List of ClassType of arguments, null values allowed.
* @param exactMatch is equals or isAssignableFrom used.
* @return List of Constructors that match the argumentTypes.
*/
private static List> matchAllConstructors(Class clazz, Class[] argTypes, boolean exactMatch) {
List> result = new ArrayList<>();
for (Constructor constructor : clazz.getConstructors()) {
if (constructor.getParameterTypes().length == argTypes.length && matchParameterTypes(constructor.getParameterTypes(), argTypes, exactMatch)) {
result.add(constructor);
}
}
return result;
}
/**
* Method to determine if the 2 lists of class types are compatible taking into account null values. Matching
* handles null values in the argTypes and consider them as compatible.
* exactMatch is true -> Classes must be equals
*
exactMatch is false -> isAssignableFrom is used (subTypes also considered compatible)
*
* @param parameterTypes List of ClassType of a method. No null values allowed.
* @param argTypes List of ClassType of arguments, null values allowed.
* @param exactMatch is equals or isAssignableFrom used.
* @return Do all arguments match the parameter types.
*/
private static boolean matchParameterTypes(Class[] parameterTypes, Class[] argTypes, boolean exactMatch) {
boolean result = true;
for (int i = 0; i < parameterTypes.length; i++) {
if (argTypes[i] != null) {
if (exactMatch) {
if (!parameterTypes[i].equals(argTypes[i])) {
result = false;
}
} else {
if (!parameterTypes[i].isAssignableFrom(argTypes[i])) {
result = false;
}
}
}
}
return result;
}
/**
* Instantiate the class using the supplied {@link Constructor} and arguments. Arguments are valid for the Constructor
* due to the logic defined in {@link #matchParameterTypes(Class[], Class[], boolean)}
*
* @param ctor Constructor to be used for instantiating the class.
* @param args The arguments for the constructor
* @param Convenience generic typecasting so no cast is needed.
* @return The new instance.
*/
private static T instantiate(Constructor ctor, Object... args) {
try {
return (T) ctor.newInstance(args);
} catch (Exception e) {
String msg = String.format("Unable to instantiate Permission instance with constructor [%s]", ctor);
throw new InstantiationException(msg, e);
}
}
/**
* Defines the capabilities of the Class Loader accessor.
*/
private interface ClassLoaderAccessor {
/**
* Tries to load the class defined by the FQCN and returns null if class is not found.
* Security Check: Make sure that the loaded class name is controlled by developer (so no arbitrary class loaded)
*
* @param fqcn FQCN of the class to load.
* @return The class corresponding ith the FQCN or null if not found.
*/
@SecurityReview
Class loadClass(String fqcn);
/**
* Tries to locate and open the resource defined by the name and returns null if not found.
*
* @param name The name of the resource to open.
* @return An InputStream to the resource or null if not found.
*/
InputStream getResourceStream(String name);
List getResources(String name);
}
/**
* An implementation that implement the {@link ClassLoaderAccessor} functionality for any classLoader but
* converts the possible {@link Exception}s to null return values.
*/
private abstract static class ExceptionIgnoringAccessor implements ClassLoaderAccessor {
@Override
public Class loadClass(String fqcn) {
Class clazz = null;
ClassLoader cl = getClassLoader();
// When there was an issue retrieving the ClassLoader, the method return null.
if (cl != null) {
try {
// Security check : Dynamic loaded class can only be from classpath (so no arbitrary class loaded)
//
clazz = cl.loadClass(fqcn);
} catch (ClassNotFoundException e) {
if (log.isTraceEnabled()) {
log.trace(String.format("Unable to load clazz named [%s] from class loader [%s]", fqcn, cl));
}
}
}
return clazz;
}
@Override
public InputStream getResourceStream(String name) {
InputStream is = null;
ClassLoader cl = getClassLoader();
// When there was an issue retrieving the ClassLoader, the method return null.
if (cl != null) {
is = cl.getResourceAsStream(name);
}
return is;
}
/**
* Retrieves the ClassLoader but but catches any Exception and logs them.
*
* @return The ClassLoader or null when there was an Exception.
*/
final ClassLoader getClassLoader() {
try {
return doGetClassLoader();
} catch (Exception e) {
if (log.isDebugEnabled()) {
log.debug("Unable to acquire ClassLoader.", e);
}
}
return null;
}
@Override
public List getResources(String name) {
ClassLoader classLoader = doGetClassLoader();
try {
return Collections.list(classLoader.getResources(name));
} catch (IOException e) {
if (log.isDebugEnabled()) {
log.debug(String.format("Unable to read resources %s from ClassLoader %s.", name, classLoader), e);
}
}
return Collections.emptyList();
}
/**
* Subclasses should implement this class and return a {@link ClassLoader}.
*
* @return {@link ClassLoader} to be used by this class.
*/
protected abstract ClassLoader doGetClassLoader();
}
}